1. The Field of the Invention
The present invention relates to a battery condition detecting apparatus that detects cancellation of a polarization of a battery installed on an automotive vehicle or a truck, especially to a battery condition detecting apparatus that detects cancellation of a polarization generated in the battery during charging of the battery.
2. Description of the Prior Art
There is a known prior art of a battery condition detecting apparatus that detects a cancellation of the charge polarization of a battery which is installed on an automotive vehicle or a truck after the battery starts to discharge, wherein the charge polarization is generated in the battery during charging of the battery. For example, such an apparatus is disclosed in Japanese Patent Laid-Open No. 2002-184469. The apparatus described in the Japanese Patent Laid-Open No. 2002-184469, an integrated charged capacity is calculated by integrating an instantaneous charged capacity from a time when charging of the battery starts to a further time when a negative acceleration of charging current changes in its sign from negative to zero. Then, after the battery starts to discharge, if an integrated discharged capacity becomes to be equal to the integrated charged capacity which is estimated just before a start of discharging of the battery, it is determined that the charge polarization generated during charging of the battery is completely canceled.
However, the known prior art of the apparatus described in the Japanese Patent Laid-Open No. 2002-184469, which is used to detect the charge polarization generated during charging of the battery, has the following problems:
(i) the apparatus that is used to detect the charge polarization generated during charging of the battery, is arranged far from a sensor. Further, a battery is located inside the engine compartment of an automotive vehicle. In general, noise such as ignition noise which occurs when the engine is ignited is generated in the engine room, that is, not far from the sensor. This means that the noise is easily superimposed on an electric signal from the sensor so as to make it difficult to accurately detect a time when a negative acceleration of charging current changes in its sign from negative to zero. If a periodic noise such as a periodic ignition noise which is caused periodically at intervals, and the interval of the periodic noise agrees with that of detecting an electric current by a sensor, an offset error is occurred in detecting the electric current. This leads to generate an error in estimating the integrated charged capacity and further to make a wrong judgment about whether or not the charge polarization of the battery is cancelled,
(ii) it is necessary to provide the apparatus with an additional electric load in order to keep a constant rate of discharge of the battery. Therefore, the electric load needs an extra space somewhere in the vehicle to be mounted. Further, the electric load consumes electric power unnecessarily,
(iii) there are methods for supplying electric power after the electric load is set up, for example. For example, there is a method in which the electric load is composed of a plurality of load elements and the start of supplying electric power to the electric load is delayed until one of the predetermined load elements is activated. Then a method is employed to calculate the integrated charged capacity. There is a further method in which even if the electric load does not reach a steady state thereof because a sufficient time is not elapsed since the electric load was switched on, simply integrating a detected charged capacity is carried out in order to calculate the integrated charged capacity. However, these methods give results in which necessary times for canceling the charge polarization of the battery are scattered and changes of degrees of cancellation of the charge polarization of the battery in time are also scattered. Therefore, it is hard to accurately detect the cancellation of the charge polarization of the battery.